1. Field of Invention
The present invention relates to an actuator for a disk drive.
2. Description of the Related Art
Developments in personal computers, portable computers and lap top computers have prompted reductions in the size and increases in memory capacity of disk drives. Existing disk drives, however, suffer from several disadvantages, and attempts to provide further reductions in size, and weight and increases in durability and memory capacity have been hampered by these disadvantages.
Existing disk drives require a large number of mechanical parts. Each additional part in a disk drive represents an increase in the possibility and probability of the mechanical failure of the drive Furthermore, each part in a disk drive represents an increase in the weight of the drive and the space occupied by the drive, and the decrease in the ability of the drive to survive physical shocks and vibrations.
Resistance to physical shocks and vibrations is critical to protecting the disk or disks, the head or heads, and the various bearings in a disk drive from damage; in particular, damage to the disks which can cause a loss of data, and damage to the heads or the bearings which can end the life of a drive, resulting in a total loss of data. Prior disk drives, however, have limited resistance to physical shocks.
Another problem with prior disk drives is the difficulty in sealing the drive to protect the disks from contaminants. This difficulty arises from the large area which must be sealed to protect the environment where the disk resides and from the large number of points at which access is provided to the environment in which the disk resides. These access points are utilized to bring to the interior of the disk drive electrical circuits which provide current to the motor which rotates the disk, transmit data signals to and from heads which read and record information on the disks, and in some instances, provide current to a voice coil for positioning the head (or heads) with respect to the disk or disks.
Many of these disadvantages of prior disk drives are attributable to the casing--a three-dimensional casting or so-called "toilet bowl"--in which the disks reside. Such a casing is a large, three dimensional piece of cast metal, usually aluminum, having a round portion where the disks reside--hence the name "toilet bowl." A top plate covers the entire open top of the casing, forming a seal therewith. The seal between the casing and the cover has a large area due to the large opening at the top of the casing. Furthermore, the spindle on which the disks rotate extends through both the casing and the cover.
Both the seal and the protrusion of the spindle through the casing and the cover provide possible points of entry for contaminants. Further, in disk drives using stepper motors to position the heads with respect to the disk, the stepper motor is located outside of the casing, requiring another seal between the stepper motor and the casing. Acknowledging the existence of points where contaminants can enter the disk drive, manufacturers of conventional disk drives provide a breather filter and design the disk drives so that the rotation of the disks causes the disk drives to exhaust air through leaks in the seals and to intake air only through the filter provided in the breather filter. However, a fairly course filter must be provided in the breather filter for a flow of air to exist, and thus contaminants can enter the disk drive through the filter paper.
A cast casing is difficult to manufacture with precision, particularly the location of mounting points for elements of the drive supported by the casing. Mounting holes must be drilled after the casing is cast, and the mounting holes must be aligned with the casing and with each other. More importantly, however, a three-dimensional, cast casing flexes due to thermal stresses. Flexing of the casing causes tracking problems by moving the heads, which are mounted at one point on the casing, relative to the disk, which is mounted at another point on the casing. In multi-disk disk drives the heads associated with different disks can move relative to the disks to the point where different heads are in different cylinders--a cylinder being defined as a vertical segment representing the same track on the respective disks. This problem is compounded by increased track densities.
An additional problem associated with known disk drives is their susceptibility to damage caused by physical shocks. This susceptibility to damage is attributable, at least in part, to the fact that the spindle on which the disks rotate is mounted directly to the cast casing.
In conventional disk drives having a cast casing and utilizing a voice coil to position the head with respect to the disk, the voice coil is a unit with a large number of elements including a permanent magnet to provide a magnetic field, separate pieces of magnetically permeable material which provide a return for the magnetic field, and a coil for carrying an electric current; the aluminum casing is not magnetically permeable and cannot be utilized as a return for the magnetic field. The separate pieces of magnetically permeable material add weight and complexity to the disk drive and require additional space. Further, the permanent magnet is mounted vertically, i.e., in a plane perpendicular to the plane of the disks, and to maintain a constant spacing between the magnet and the coil, which is mounted on a pivoting arm, the magnet must be curved, increasing manufacturing cost and difficulty.
Various types of locking (or latch) devices have been used to lock the arm of a voice coil in a particular position when the disk drive is not operating. The trend in latch devices is to utilize a high power unit which is separately assembled to provide reliability. However, high power latch devices generate a large amount of heat which is not desirable in a disk drive or any other area in a computer. Further, the operation of conventional latch devices can be position dependent. Thus, the orientation of the disk drive could effect the reliability of the latch device.